29 Sep

Understanding how the heat propagates in a material is a key issue in many different fields. For application such as nano and micro technology, heat dissipation is a key element. For thermoelectric materials, which can transform heat into electricity, researchers design new materials and try to reduce as much as possible their thermal conductivity, a key parameter in the efficiency equation in these materials. However an understanding of the deta... [...]

26 Sep

A comparative study has been performed on the adsorption of structurally related but stereochemically different C60 and C20H10 molecules on the 5-fold surface of the icosahedral i-Ag-In-Yb quasicrystal. Both molecules have similar lateral dimensions and have the same pentagonal carbon ring surrounded by five phenyls. However, while C60 molecules have 2-, 3- and 5-fold rotational symmetries, C20H10 only have C5v symmetry. Therefore both organic mo... [...]

27 Nov

The cage compound Ba3Ge16Ir4 crystallizes with the Ba3Ge16Rh4 type of crystal structure, which represents a hierarchical derivative of the BaAl4 type. The crystal structure [Pearson symbol tI46, space group I4/mmm; a = 6.5312(2) Å, c = 22.2845(6) Å] was refined from single-crystal X-ray diffraction data. The phase was obtained after 10 d at 910 °C with small impurities of clathrate-I, BaGe7Ir2 and α-Ge remaining at the grain boundaries.... [...]

06 Jan

A paradigm for the one-step formation of complex intermetallic coatings by chemical vapor deposition has recently been published by CNRS in Toulouse. The work genuinely addresses the challenge of depositing an intermetallic coating with comparable contents of Cu and Al. Depending on processing conditions, a pure gamma-Al4Cu9 and multi-phaseAl-Cu films are grown with wetting properties of the former being similar to its bulk counterpart. The... [...]

21 Nov

An international collaboration led by the University of Liverpool has discovered an exotic film of the element lead (Pb), in which the atoms are arranged in pentagonal and decagonal structures rather than in the usual cubic fashion. Quasicrystals, the discovery of which led to the award of the 2011 Nobel Prize in Chemistry to Dan Shechtman of the Technion Institute, Israel, were first observed in alloyed systems comprising several elements.... [...]

12 Mar

PHONONIC FILTER EFFECT IN THE BA-GE-NI CLATHRATE SYSTEM
Intermetallic clathrates are so called cage compounds. Their structure can be described by a host framework, consisting of large cages, which enclose heavy guest atoms (see Fig. 1). While clathrates exhibit a crystal-like electrical conductivity, their thermal conductivity is strongly reduced making them promising materials for thermoelectric application. So far, the microscopic me... [...]

28 Nov

The quasicrystal approximant Zn6Sc: a surprising dynamical flexibility
Quasiscrystals are materials in which the atoms are arranged in such a manner that long range order is maintained, however, without periodicity, and thus in contrast to conventional crystals. To better understand the structure and the way atoms move inside a quasicrystal, an international team of European and Japanese scientists (European C-MAC network, www.eucmac.eu)... [...]

08 Oct

An iron-aluminium compound could replace a palladium catalyst, reducing the cost of plastic production
Chemists don't like precious metals – at least not when they need the expensive materials as catalysts to accelerate reactions or guide them in a particular direction. And this is often the case, as in an important step in the production of polyethylene, a substance that makes plastic bags light, flexible and stable. However, an international... [...]

09 May

A detailed study of the (001) surface of the Al2Cu crystal using both experimental and ab initio computational methods is presented in this work. The combination of both approaches gives many arguments to match the surface plane with a bulk truncated surface model terminated by incomplete Al planes. The missing rows of Al atoms lead to a 2 root2 x root2 R 45° surface reconstruction with two domains rotated by 90 from each other. Ab initio calcu... [...]

06 Mar

Methanol steam reforming (MSR, CH3OH + H2O à 3H2 + CO2) is considered as one of the most promising routes to produce high purity hydrogen for mobile fuel cell applications. However, the main drawback is the formation of CO as a byproduct, which has to be kept at a level of about 10 ppm to prevent poisoning of fuel cell catalysts.
MSR on single-phase samples of the intermetallic compound ZnPd, all possessing the CuAu type of crystal structure, p... [...]

15 Jun

We have extensively studied Mg2Zn11, a compound which shows interesting vibrational properties and exhibits intermediate structural complexity in between the Laves phase MgZn2 and alloys of higher complexity or quasicrystals .
The structure can be described as a cubic packing of a triacontahedron whose center is partially occupied by a Zn atom. This partially occupied site turned out to play a major role in understanding the lattice dynamics. Th... [...]

16 Feb

Among the three coexisting types of terraces found on the twofold surface of the d-Al-Cu-Co quasicrystal, nanodomains are essentially observed on the transition-metal rich ones, with a coherent interface boundary. Both clean surface and Ag growth analyses, demonstrate that nanodomain surfaces are structurally identical to one of the two other terraces, which contains 85 at. % Al. We provide evidence that the nanodomains are a manifestatio... [...]